| Kernel driver lm90 |
| ================== |
| |
| Supported chips: |
| * National Semiconductor LM90 |
| Prefix: 'lm90' |
| Addresses scanned: I2C 0x4c |
| Datasheet: Publicly available at the National Semiconductor website |
| http://www.national.com/pf/LM/LM90.html |
| * National Semiconductor LM89 |
| Prefix: 'lm99' |
| Addresses scanned: I2C 0x4c and 0x4d |
| Datasheet: Publicly available at the National Semiconductor website |
| http://www.national.com/pf/LM/LM89.html |
| * National Semiconductor LM99 |
| Prefix: 'lm99' |
| Addresses scanned: I2C 0x4c and 0x4d |
| Datasheet: Publicly available at the National Semiconductor website |
| http://www.national.com/pf/LM/LM99.html |
| * National Semiconductor LM86 |
| Prefix: 'lm86' |
| Addresses scanned: I2C 0x4c |
| Datasheet: Publicly available at the National Semiconductor website |
| http://www.national.com/pf/LM/LM86.html |
| * Analog Devices ADM1032 |
| Prefix: 'adm1032' |
| Addresses scanned: I2C 0x4c and 0x4d |
| Datasheet: Publicly available at the Analog Devices website |
| http://www.analog.com/en/prod/0,2877,ADM1032,00.html |
| * Analog Devices ADT7461 |
| Prefix: 'adt7461' |
| Addresses scanned: I2C 0x4c and 0x4d |
| Datasheet: Publicly available at the Analog Devices website |
| http://www.analog.com/en/prod/0,2877,ADT7461,00.html |
| Note: Only if in ADM1032 compatibility mode |
| * Maxim MAX6657 |
| Prefix: 'max6657' |
| Addresses scanned: I2C 0x4c |
| Datasheet: Publicly available at the Maxim website |
| http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578 |
| * Maxim MAX6658 |
| Prefix: 'max6657' |
| Addresses scanned: I2C 0x4c |
| Datasheet: Publicly available at the Maxim website |
| http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578 |
| * Maxim MAX6659 |
| Prefix: 'max6657' |
| Addresses scanned: I2C 0x4c, 0x4d (unsupported 0x4e) |
| Datasheet: Publicly available at the Maxim website |
| http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2578 |
| |
| |
| Author: Jean Delvare <khali@linux-fr.org> |
| |
| |
| Description |
| ----------- |
| |
| The LM90 is a digital temperature sensor. It senses its own temperature as |
| well as the temperature of up to one external diode. It is compatible |
| with many other devices such as the LM86, the LM89, the LM99, the ADM1032, |
| the MAX6657, MAX6658 and the MAX6659 all of which are supported by this driver. |
| Note that there is no easy way to differentiate between the last three |
| variants. The extra address and features of the MAX6659 are not supported by |
| this driver. Additionally, the ADT7461 is supported if found in ADM1032 |
| compatibility mode. |
| |
| The specificity of this family of chipsets over the ADM1021/LM84 |
| family is that it features critical limits with hysteresis, and an |
| increased resolution of the remote temperature measurement. |
| |
| The different chipsets of the family are not strictly identical, although |
| very similar. This driver doesn't handle any specific feature for now, |
| with the exception of SMBus PEC. For reference, here comes a non-exhaustive |
| list of specific features: |
| |
| LM90: |
| * Filter and alert configuration register at 0xBF. |
| * ALERT is triggered by temperatures over critical limits. |
| |
| LM86 and LM89: |
| * Same as LM90 |
| * Better external channel accuracy |
| |
| LM99: |
| * Same as LM89 |
| * External temperature shifted by 16 degrees down |
| |
| ADM1032: |
| * Consecutive alert register at 0x22. |
| * Conversion averaging. |
| * Up to 64 conversions/s. |
| * ALERT is triggered by open remote sensor. |
| * SMBus PEC support for Write Byte and Receive Byte transactions. |
| |
| ADT7461 |
| * Extended temperature range (breaks compatibility) |
| * Lower resolution for remote temperature |
| |
| MAX6657 and MAX6658: |
| * Remote sensor type selection |
| |
| MAX6659 |
| * Selectable address |
| * Second critical temperature limit |
| * Remote sensor type selection |
| |
| All temperature values are given in degrees Celsius. Resolution |
| is 1.0 degree for the local temperature, 0.125 degree for the remote |
| temperature. |
| |
| Each sensor has its own high and low limits, plus a critical limit. |
| Additionally, there is a relative hysteresis value common to both critical |
| values. To make life easier to user-space applications, two absolute values |
| are exported, one for each channel, but these values are of course linked. |
| Only the local hysteresis can be set from user-space, and the same delta |
| applies to the remote hysteresis. |
| |
| The lm90 driver will not update its values more frequently than every |
| other second; reading them more often will do no harm, but will return |
| 'old' values. |
| |
| PEC Support |
| ----------- |
| |
| The ADM1032 is the only chip of the family which supports PEC. It does |
| not support PEC on all transactions though, so some care must be taken. |
| |
| When reading a register value, the PEC byte is computed and sent by the |
| ADM1032 chip. However, in the case of a combined transaction (SMBus Read |
| Byte), the ADM1032 computes the CRC value over only the second half of |
| the message rather than its entirety, because it thinks the first half |
| of the message belongs to a different transaction. As a result, the CRC |
| value differs from what the SMBus master expects, and all reads fail. |
| |
| For this reason, the lm90 driver will enable PEC for the ADM1032 only if |
| the bus supports the SMBus Send Byte and Receive Byte transaction types. |
| These transactions will be used to read register values, instead of |
| SMBus Read Byte, and PEC will work properly. |
| |
| Additionally, the ADM1032 doesn't support SMBus Send Byte with PEC. |
| Instead, it will try to write the PEC value to the register (because the |
| SMBus Send Byte transaction with PEC is similar to a Write Byte transaction |
| without PEC), which is not what we want. Thus, PEC is explicitely disabled |
| on SMBus Send Byte transactions in the lm90 driver. |
| |
| PEC on byte data transactions represents a significant increase in bandwidth |
| usage (+33% for writes, +25% for reads) in normal conditions. With the need |
| to use two SMBus transaction for reads, this overhead jumps to +50%. Worse, |
| two transactions will typically mean twice as much delay waiting for |
| transaction completion, effectively doubling the register cache refresh time. |
| I guess reliability comes at a price, but it's quite expensive this time. |
| |
| So, as not everyone might enjoy the slowdown, PEC can be disabled through |
| sysfs. Just write 0 to the "pec" file and PEC will be disabled. Write 1 |
| to that file to enable PEC again. |